The present invention relates to an apparatus for wrapping palletized stacks of commodities in a plastic film material.
There are currently numerous machines of the type in question available for purchase (typically as disclosed in Italian patent 1 179 310), consisting generally in a load-bearing frame of gantry type construction, and a beam of upturned `L` profile suspended rotatably from the center of the frame by the horizontal member of the `L` and set in motion by a drive system. The vertical member of the `L` carries a station serving to support a roll of the plastic wrapping film; as a rule this same station is also capable of a controlled traversing movement on the vertical member of the beam, such that the stacked commodities can be enveloped to their full height.
The palletized stacks of commodities for wrapping are positioned at the center of the apparatus, or rather the center of the gantry, either by a pallet lift truck (in the case of more simple equipment), or by means of a permanently installed horizontal conveyor running at floor level directly beneath the gantry; once the pallet is at a standstill in the required position, a restraint device will be activated in such a way as to descend and stabilize the entire pallet load by engaging the top face of the stack of commodities. Thereupon, the free end of the film is secured to the pallet base or held fast by means of a gripper mechanism, and the drive system is activated: the upturned `L` beam begins circling the pallet, and the stacked commodities are enveloped gradually by the uncoiling film. Where the width of the film is less than the height of the stacked commodities (as will normally be the case), the roll of film naturally must be made to ascend and descend on the vertical member of the beam to ensure that the commodities are enveloped completely from top to bottom. In most instances the plastic film is stretched during the wrapping operation (by applying a braking action to the roll) to the ends of achieving a certain saving on the cost of the wrapping material utilized, and of increasing the tension of the wrapping in order to enhance its ultimate tightness around the pallet, especially where the commodities are stacked high. The main drawbacks besetting such apparatus derive for the most part from the significant bulkiness of the gantry frame, which has to carry the `L` beam and its drive system, together with the relative transmission components. As a direct consequence, the entire apparatus is rendered especially heavy, not least by reason of the fact that the center of the masses in rotation lies high up in the frame, demanding suitably proportioned reaction elements to offset the forces generated in operation. A further drawback, stemming from the first, is the need to maintain a low wrapping speed precisely in order to limit the mechanical stresses generated in rotation.
Accordingly, the object of the present invention is to overcome the drawbacks briefly outlined above, by providing an apparatus for wrapping palletized stacks of commodities such as will ensure a swift, precise wrapping action and faster operation per unit of mass, while featuring compact dimensions and advantages of economy.